Can anyone tell me if a 220 gr engine weight difference will have a significant effect on the CG in a 7.5 pound plane. Thanks.

That's almost 8 ounces. Yes it will affect the CG. Significant? It could push it out of the recommended CG range.

It's the same as adding or taking off 2-3 ounces from the tail.

The change in cg is
cg shift = (increase in engine weight/ plane weight) times distance from cg to engine

For a typical 7 lb plane adding 0.5 lb engine wt will move the cg about 1 to 1.5 inches forward.

Thanks guys. I got a YS1.20SF (950gr) in a Seagull Harrier (8.5#'s). My CG needs to go back some I think. I'm thinking of switching to a YS1.10 (730gr).

The effect of weight added on cg depends on how far it is added from the the cg. Adding a few ozs near the tail will move the cg back as much as removing 4-8 ozs from the engine . I would tape on a couple of ozs to the fuse as far aft as is convenient and see how I liked it. That is a lot easier than changing engines and easier to tinker with to get what you want.

I totally agree. It's much better to put 2-3 ounces in the tail of a nose-heavy ARF than it is to add 8-9 ounces in the nose of tail-heavy ARF. You save all up weight. Also replacing the engine is a major operation. Just add a little tail weight until it's where you want it. When you get too tail heavy, the plane starts to drag it's tail around and forward speed suffers. It's also a pain to land. Move it back in little increments (add 1/2 to 1 ounce at a time).